1. Field of the Invention
This invention relates to apparatus for manufacturing folding carton blanks and, more specifically, to apparatus for folding the trailing panels of such carton blanks.
2. Background
In machines for folding blanks successively and individually, the blanks travel through a series of stations. Apparatus at each station performs, sequentially, some folding, gluing or other operation on individual panels formed on the blanks as successive blanks pass that station. A conveyor system transports the blanks past each station in seriatim, normally on a "paper line".
Folding operations require a trailing panel to be folded forward (i.e., in the direction of travel of the conveyor) about a fold line that is transverse to the paper line. Trailing panel folding operations present special problems in carton folding because the blank must pass the folding station before the apparatus can engage and fold the panel
Some systems fold trailing panels by using a so-called "right angle" paper line. Essentially, the apparatus folds and glues all panels on the front and sides along a first paper line Then the apparatus directs the blanks to a second paper line that runs at right angles to the first paper line. If the orientation of the blank in space remains the same during the transfer, the trailing panel on the first line becomes a side panel on the second line and can be folded as a convent side panel. This apparatus has several drawbacks. First, the transfer from one line to another requires care often achieved by increasing the spacing between blanks and slowing conveyor speed. This reduces machine throughput. Moreover, right-angle systems generally require more floor area than straight-line systems; consequently overheads increase, so this apparatus is more costly to operate.
There has been an effort to develop trailing panel folding stations that operate in a straight-line, or in-line, apparatus. The following U.S. Letters Patent disclose prior efforts:
U.S. Pat. No. 3,330,185 (1967) Annett et al PA1 U.S. Pat. No. 3,901,134 (1975) Reizenstein et al PA1 U.S. Pat. No. 4,119,018 (1978) Nava PA1 U.S. Pat. No. 4,432,745 (1984) Eldridge PA1 U.S. Pat. No. 4,539,002 (1985) Zak PA1 U.S. Pat. No. 4,715,846 (1987) Zak
Annett et al disclose a box folding machine apparatus. A cam mechanism driven from a shaft rapidly accelerates an arm on a head to overtake a rear panel and fold it on top of a blank.
In accordance with Reizenstein et al, a clutch has an input connected to the main drive of the folding box apparatus and an output connected to a secondary drive for an endless operating loop. A sensing means responds as each blank passes a reference point by causing the clutch to engage and initiate motion of the endless operating loop that is synchronized to the position of the blank. Folding fingers pivotally connect to the loop and have cam followers that engage a stationary cam. Each finger moves into contact with a box blank at the trailing panel as the cam follower contacts the cam. A second sensing means and related apparatus disengage the clutch when the folding finger reaches a predetermined position after completing the folding operation.
Nava discloses a system with a trailing edge sensor that initiates the operation of a folding head with a cam control element. This control element moves folding fingers with an appropriate velocity profile to engage and fold a trailing panel The mechanism includes a shaft for the folding heads, an idler shaft that carries the cam, a braking mechanism and a clutch.
Eldridge discloses a trailing panel folding machine with a two-armed head that rotates one-half revolution each time it folds a trailing panel. A drive motor and clutch-brake assembly drive the head. The clutch-brake comprises an electromechanical or a pressure- or vacuum-operated mechanical device. A variable speed electric motor rotates the head at a speed dependent upon the length of the blanks. Alternatively it is suggested to tie the drive to the conveyor drive motor thereby to compensate any changes in conveyor speed.
When Eldridge's clutch-brake engages, the head rotates at the speed of the drive for 180.degree. (i.e., the angle needed to perform one folding operation). When the clutch-brake disengages, the head stops rotating. A sensor determines the position of a blank as it travels along a conveyor. The resulting position information and conveyor speed information establish timing for engaging the clutch-brake mechanism and initiating a two-step folding cycle. The drive head begins at a starting or dwell position with the clutch-brake disengaged. During a first step, a signal from an electronic controller causes the clutch-brake to engage and rotate the head to fold the trailing panel and then to disengage and stop the head in an intermediate position. This allows the blank to pass from the folding station. After another interval, that assures that the blank has cleared this station, the controller initiates the second step during which the clutch-brake engages to move the folding head to a separate home position below the paper line where the head dwells in preparation for the next blank.
The Zak-002 patent discloses a trailing panel folding apparatus in which folding heads connect to a drive through a clutch-brake that responds to various control signals. When the trailing edge of a blank passes a predetermined position, the signals cause the clutch to engage and rotate folding fingers on the heads and fold the trailing panel. Then the stop and subsequently rotate again to a dwell position to complete a two-step folding operation.
The Zak-846 patent discloses a trailing panel folding apparatus in which a servomotor directly drives a shaft carrying two folding heads. Each head has a pair of radially extending arms that engage and fold the trailing panels of successive blanks. A computer and programmable motor controller directly control the rotation and velocity profiles of the servomotor in a two-step cycle comprising a fold step and a return step. During the fold step, one arm starts below the conveyor and rotates at an appropriate time to engage the trailing panel and fold it over. In a vertical position, the drive shaft dwells to allow the blank to exit from under the folding arm. Then the return step positions the second arm just below the conveyor so it is oriented at the starting position.
These embodiments of apparatus for folding a trailing edge or panel have some common characteristics. First, they all, except for the apparatus with Zak-846 patent, contain mechanisms that must physically engage and disengage. These operations require finite time intervals that, in part, are determined by the momentum changes inherent whenever an element starts and stops. This apparatus, particularly including the apparatus of the Zak-846 patent, involves significant rapid and repeated changes in momentum, particularly as the mass of the elements involved is significant and the process is iterative in nature. These requirements can impose limits on parameters such as minimum blank spacing and maximum conveyor speed that individually and collectively limit throughput.
For example, the conveyor speed for in-line apparatus is generally a function of the capabilities of the trailing panel folding apparatus to accelerate, engage and overtake the blank and then to stop so the folded blank can exit. This, in turn, depends upon the physical inertia of the folding system and the characteristics of various elements, such as motors, used to drive the folding element. Minimum spacing between successive blanks depends, in part, upon the time interval required to move the folding element from a dwell position above a paper line to a position below the paper line that allows the next blank to enter the backfolding station. This interval also depends on the physical inertia of the folding element and its associated drive mechanism and the ability of the drive system accelerate and decelerate.